The present invention generally relates to an acoustic protective cover for a transducer (such as a microphone, ringer or speaker) employed in an electronic device. More specifically, the present invention relates to an acoustic protective cover assembly including a microporous protective membrane that provides both low acoustic loss and the ability to withstand long-term exposure to liquid intrusion.
Most modern electronic devices, such as radios and cellular telephones, include transducers, e.g., microphones, ringers, speakers, buzzers and the like. These electronic devices often comprise housings having small apertures or holes located over the transducers to enable the transducers to transmit or receive sound signals from within the housing. However, although this configuration protects against incidental exposure to water (e.g., a raindrop), it excessively attenuates a transducer""s effectiveness and sound quality. Furthermore, it cannot resist the entry of a significant amount of water. Accordingly, acoustic protective covers have been utilized between the transducers and the housing to protect the transducers from damage due to the entry of water or other liquids.
Prior art acoustic protective covers are typically composed of a porous, fabric material constructed solely on reducing the material""s resistance to air flow of which larger effective pore size resulting in thicker materials has been the means for achieving the high air flow parameters. Here, the amount of sound attenuation of the material is inversely proportional to the size of its pores, i.e., sound attenuation decreases as pore size increases. However, the size of the pores oppositely affects the water resistance of the material. Materials having extremely small or no pores are highly water resistant.
Thus, prior art acoustic protective covers have focused on having either large pores for enhanced sound transmission and quality, or extremely small pores and tighter structure for high water resistance. A focus on the former results in an acoustic protective cover that at best provides an electronic device minimal protection against exposure to water. A focus on the latter protects the electronic device from larger amounts of water, but results in poor sound quality due to high sound attenuation. Even the treatment of the porous materials for water repellency fails to permit immersion of the electronic device to significant depths because of the large pore structure.
A general description of prior art patents adhering to the above-described scientific principle follows.
U.S. Pat. No. 4,949,386, entitled xe2x80x9cSpeaker System,xe2x80x9d teaches an environmental protective covering system, comprising in part a laminated two-layer construction defined by a polyester woven or non-woven material and a microporous polytetrafluoroethylene (xe2x80x9cPTFExe2x80x9d) membrane. The hydrophobic property of the microporous PTFE membrane prevents liquid from passing through the environmental barrier system. However, although this laminated covering system may be effective in preventing liquid entry into an electronic device, the lamination causes excessive sound attenuation which is unacceptable in modern communication electronics where excellent sound quality is required. Furthermore, while it is effective at preventing instantaneous liquid entry, long-term liquid exposure is limited because of eventual breakdown of the adhesive/membrane interface.
U.S. Pat. No. 4,987,597, entitled xe2x80x9cApparatus For Closing Openings Of A Hearing Aid Or An Ear Adaptor For Hearing Aids,xe2x80x9d teaches the use of a microporous PTFE membrane as a covering for an electronic transducer. The membrane restricts liquid passage through the membrane without significantly attenuating sound signals. However, the patent fails to specifically teach which material parameters of the membrane are required in order to achieve both low sound loss and long-term exposure to liquid entry, although it does generally describe the parameters in terms of porosity and air permeability.
U.S. Pat. No. 5,420,570, entitled xe2x80x9cManually Actuable Wrist Alarm Having A High-Intensity Sonic Alarm Signal,xe2x80x9d teaches the use of a non-porous film as a protective layer to protect an electronic device from liquid entry. As previously discussed, although a non-porous film can provide excellent liquid entry resistance, such non-porous films suffer from relatively high sound transmission losses which excessively distort sound signals. The increase in transmission loss results from the relatively high mass associated with non-porous films.
U.S. Pat. No. 4,071,040, entitled xe2x80x9cWater-Proof Air Pressure Equalizing Valve,xe2x80x9d teaches the disposition of a thin microporous membrane between two sintered stainless steel disks. Although such a construction may have been effective for its intended use in rugged military-type field telephone sets, it is not desirable for use in modern communication electronic devices because the sintered metal disks are relatively thick and heavy. Furthermore, disposing a microporous membrane between two stainless steel disks physically constrains the membrane, thereby limiting its ability to vibrate, which reduces sound quality by attenuating and distorting a sound signal being transmitted.
To overcome some of the shortcomings described above with respect to the ""386, ""597, ""570 and ""040 patents, U.S. Pat. No. 5,828,012, entitled xe2x80x9cProtective Cover Assembly Having Enhanced Acoustical Characteristics,xe2x80x9d teaches a sound-transmissive acoustic cover assembly that has a protective membrane that is bonded to a porous support layer so that an inner unbonded region surrounded by an outer bonded region is formed. In this configuration, the membrane layer and the support layer are free to independently vibrate or move in response to acoustic energy passing therethrough, thereby minimally attenuating the acoustic energy. However, although the cover assembly reduces the acoustic attenuation, the degree of acoustic attenuation is limited because of the increase in material mass and thickness by which the acoustic energy has to pass (i.e., acoustic energy has to first pass through the membrane, and then additionally pass through the support layer).
Finally, Japanese Laid Open Patent Application No. 10-165787, entitled xe2x80x9cPorous Polytetrafluoroethylene Film And Manufacturing Process For Same,xe2x80x9d teaches the use of a porous PTFE film to protect an electronic device from liquid entry while maintaining sound permeability. A longitudinally-stretched PTFE membrane is coated on one or both sides with a thermoplastic resin netting that functions as both a reinforcing material and a shape stabilizing material. Using this manufacturing method, the size of the pores in the film uniformly expand to improve sound permeability by means of the thinning of the membrane without compromising the film""s water resistance. Such a porous PTFE film exhibits sound attenuation of no more than 1 dB for frequencies of 300-3000 Hz (i.e., the range of frequencies known as the xe2x80x9ctelephony rangexe2x80x9d) and static water pressure resistance of 30 cm or above. However, although the PTFE film covering effects relatively low sound attenuation, overall sound transmission loss is excessive and is considered unacceptable in modern communication electronic devices. Additionally, the PTFE film lacks the ability to withstand long-term water intrusion at higher pressures.
Because the sole focus of the above-described prior art patents is on membrane porosity, the higher airflow membranes taught therein can produce low sound transmission loss but are unable to meet IP-57 level water protection as defined by the International Electrotechnical Commission (xe2x80x9cIECxe2x80x9d) (1 meter water submersion for 30 minutes). The IEC is affiliated with the International Organization for Standardization (xe2x80x9cISOxe2x80x9d), and publishes the IP Code, entitled xe2x80x9cDegrees Of Protection Provided By Enclosures,xe2x80x9d to describe a system for classifying the degrees of protection provided by enclosures for electrical equipment. One of the enumerated objects of the standard is to protect the equipment inside an enclosure against harmful effects due to the ingress of water. The IP-57 standard is described in IEC publication Reference No. 529, Second Impression, 1992.
Because the consumer market desires to use electronic devices in demanding environmental and working conditions such as exposure to long-term liquid and particle intrusion, the demand for durable, water-resistant electronic devices having a high sound quality has increased remarkably. Therefore, there exists a need for an acoustic protective cover having high airflow to allow for low sound attenuation (i.e., less than 3 dB) while providing IP-57 level protection. The acoustic protective cover should also be lightweight and sufficiently rigid for quick and accurate installation.
In addition to the foregoing, an acoustic gasket is desirable to eliminate flanking paths, structural vibrations and focus acoustic energy to the housing apertures. More particularly, if no acoustic gasket is utilized between sound transducers (loudspeakers, ringers, microphones, etc.) and the housing, acoustic energy may leak into other regions of the housing, thereby attenuating and distorting the sound energy entering or leaving the housing. Such sound energy leakage can result in attenuation and distortion of sound projected out of the housing by transducers such as loudspeakers, ringers, etc., or of sound entering the housing to actuate a microphone. Without acoustic gaskets, these acoustic losses result in reduced battery life of communication electronic devices and higher transducer output levels. Acoustic gaskets can improve the effectiveness of loudspeakers by isolating them from the housing, thereby converting more of the speaker""s mechanical energy directly into acoustic energy. Acoustic gaskets and materials are well-known in the art, however, they are usually assembled into devices as separate components and thereby increase the cost and complexity of manufacturing the devices.
The foregoing illustrates limitations known to exist in present acoustic protective covers and gasket systems for electronic communication devices. Thus, it is apparent that it would be advantageous to provide an improved protective system directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In connection with the foregoing, a sound-transmissive acoustic protective cover assembly is disclosed that protects electronic devices from long-term exposure to liquid intrusion while providing equivalent or better sound attenuation than pre-existing acoustic covers. The assembly includes a microporous protective membrane that meets IP-57 requirements with low sound loss by recognizing that the important parameters on which to focus when constructing the membrane are moving mass and thickness, not air flow. A reduction in both the moving mass and thickness of the membrane effectively reduces sound transmission loss within the telephony range.
According to one embodiment of the invention, the assembly comprises a microporous protective membrane that is captivated between two adhesive support systems. The first adhesive support system can be either a single- or double-sided adhesive, however the primary function of this adhesive support system is to anchor the membrane to the opposing adhesive support system. The second adhesive support system is a double-sided adhesive that serves as a gasket for the transducer or the housing, depending on the application. Both adhesive support systems are bonded to the membrane so that an inner unbonded region surrounded by an outer bonded region is formed on the membrane. In the unbonded region, the combination of the two adhesive support systems allows upstream sound pressure waves to vibrate the membrane and transfer the structureborne energy (mechanical vibration) of the membrane to airborne energy (pressure waves) downstream of the acoustic protective cover assembly, resulting in low acoustic loss/attenuation. In addition to minimizing transmission loss, the acoustic cover assembly provides IP-57 level water protection for the membrane discussed above. This level of water protection can be achieved because of the additional stiffness and anchoring provided to the membrane. The opposing adhesive support system prevents the assembly from structural failure caused by the membrane peeling away from the adhesive.
According to another embodiment of the present invention, the first adhesive support system is a double-sided adhesive that further incorporates a gasket to direct sound through the openings in the housing of the electronic device to account for gaps between the acoustic protective cover assembly and the device ports that can cause acoustic leakage and thereby increase the transmission loss of the device.
According to another embodiment of the invention, the protective membrane is bonded only to the second adhesive support system.
According to yet another embodiment of the invention, the protective membrane is injection-molded into a cap.
The apparatus and method of the invention will be more readily understood and apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings, and from the claims which are appended at the end of the detailed description.